1. Field of the Invention
The present invention relates to a wavelength division multiplexed optical communication system, and more particularly to a light source used for generating a plurality of optical signals having different wavelengths.
2. Description of the Related Art
In a conventional wavelength division multiplexed optical communication system, a central office provides a plurality of optical signals having different wavelengths to subscriber units, and a remote node located between the subscriber units and the central office serves to connect the central office to each subscriber unit.
The central office includes an optical transmitter for generating optical signals having different wavelengths to be transmitted to each subscriber unit. The optical transmitter includes a light source for generating a plurality of channels having predetermined wavelengths and a modulator for modulating each of the channels into an optical signal.
FIG. 1 is a block diagram showing a construction of a conventional wavelength division multiplexed (WDM) optical communication system. As shown, the WDM system includes a central office 110 for generating downstream optical signals, a plurality of subscriber units 130-1 to 130-n for generating upstream optical signals, and a remote node 120 for demultiplexing a multiplexed downstream optical signal, and multiplexing the upstream optical signals for subsequent transmission to the central office 110.
The central office 110 includes a multiplexer/demultiplexer 114, a plurality of optical transmitters 111, and photodetectors 113 to demultiplexe the multiplexed upstream optical signal received from each subscriber unit and multiplexes the downstream optical signals having different wavelengths to output the multiplexed optical signal to the remote node 120.
The multiplexer/demultiplexer 114 demultiplexes the multiplexed upstream optical signals, which are received from the remote node 120, to respective wavelengths, and the photodetectors 113 detect corresponding demultiplexed upstream optical signals.
The optical transmitters 111 may include a light source for generating channels having predetermined wavelengths and a modulator for modulating the channels. For long distance transmission, the light source may use a distributed feedback laser capable of outputting a channel having a single wavelength or an electro-absorption modulator laser including a modulator and a light source.
The remote node 120 is linked to a central office 110 through a single optical fiber and is located between the subscriber units 130-1 to 130-n and the central office 110, connecting the subscriber units 130-1 to 130-n to the central office.
Each of the subscriber units 130-1 to 130-n includes a light source 132 for generating the upstream optical signals, and a photodetector 133 for detecting a corresponding downstream optical signal, so that each subscriber unit detects the downstream optical signal and outputs the upstream optical signal to the remote node 120.
The abovementioned central office, however, includes a plurality of light sources for generating a channel having a single wavelength, thereby increasing the cost required for constructing a wavelength division multiplexed communication system. Furthermore, a number of light sources required for long distance transmission used in a local area network further increases the installation cost of such a communication network.